Dynamic Vibration Control Systems and Methods for Industrial Lift Trucks

ABSTRACT

A lift truck includes systems and methods for improved vibration control. Vibration control features reduce or eliminate motion of the truck in one or more of the X-axis, Y-axis, and Z-axis. Some embodiments may include, alone or in combination with the vibration control, stability control to further stabilize the motion of the truck.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/454,188, filed Mar. 18, 2011, and entitled“Dynamic Stability Control Systems And Methods For Industrial LiftTrucks,” which is hereby incorporated by reference.

STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to the field of industrial lift trucks,and more specifically to systems and methods for improved vibrationcontrol for lift trucks.

BACKGROUND OF THE INVENTION

Lift trucks are designed in a variety of configurations to perform avariety of tasks. A lift truck traveling throughout a facility mayencounter debris on the floor and uneven floor surfaces. These can takethe form of expansion joints, cracks in the floor surface or man-madeobjects such as ramps going between buildings or into tractor trailers.Tire irregularities and/or the floor can also cause periodic vibrationthat can be transmitted throughout the frame of the truck.

When a lift truck is traveling fast, one or more wheels strike an edgeof the uneven surface harder than when the truck is traveling slowly.The energy from this motion is transmitted throughout the truck in theform of shock waves. Referring to FIG. 1, the resultant forces may betransmitted throughout a truck 10 in any of the three axes, includingthe X-axis 12, the Y-axis 14, and the Z-axis 16, and may be felt by theoperator (not shown) creating a sense of discomfort. The truck 10 mayinclude a tractor unit 17 and vertically movable forks 19 mountedrelative to the tractor unit, the movable forks being vertically movablebetween an upper position and a lower position. If there is no operator,such as when the truck is being remotely controlled, the resultantforces may still have negative effects because equipment 18 on the truckmay be rendered less effective. If there is equipment 18 on the truck,such as sensitive sensory equipment, the quality of the data from theequipment 18 may diminish because of the resultant forces and resultanttruck reaction.

When a lift truck strikes a floor condition that affects only one side,such as when only one wheel, such as caster wheel 20, strikes a raisedcrack in the floor, and that side is forced up, the resultant motion iscommonly called roll, and is shown as movement about the X-axis 12. Theeffect of roll causes the entire truck to temporarily move or tilt toone side (to the side of the truck with the wheel that did not strikethe crack), and any sensory equipment mounted on the truck will also bedirected to the same side. Equipment 18, such as a sensor mountedseveral feet away from the original point of movement, (the caster wheel20), will have its reaction exaggerated. The sudden movement caused bythe floor condition can diminish the effectiveness and/or accuracy ofthe sensory equipment and may necessitate that the truck be operated atslower speeds to reduce the effects of the floor conditions. Sloweroperating speeds may equate to an undesirable reduction in overallequipment productivity.

Referring to FIG. 2, a variety of lift truck configurations use springloaded casters 24, including for example pallet trucks and stackertrucks, that have a center traction wheel 26 spaced between the twospring loaded casters 24. The spring loaded casters allow for drivingover rough surfaces or floors 28 while still maintaining good contactforce for the traction wheel 26. This contact force is important becauseacceleration, braking, and control are mainly achieved through thetraction wheel, so the wheel 26 should maintain floor contact withenough force to control the truck motion. Typically, the casters areadjusted to find an optimum operation between traction wheel slippageand the truck rocking or tilting between both casters.

The casters 24 can be adjusted by adding shims 30 to push down harder onthe floor, thus raising the truck slightly, or shims can be removed tomake caster springs 32 push less, thus slightly lowering the truck.Typically, the caster springs 32 themselves are not adjusted. Thepurpose of the shim 30 is to set how much of the vehicle weight is onthe traction wheel 26 versus how much is on the spring loaded casters24. Without the flexible spring loaded casters and the ability to adjustthe casters with shims, the casters may end up carrying most of theweight and the traction wheel may slip due to not enough contact force,or the traction wheel may take most of the weight, causing the truck toslightly tilt to one caster or the other.

Caster adjustment may be time consuming, and may include jacking up thetruck, estimating how big a shim to install, and then seeing if the shimwas too big or too little. In this configuration, there is no dynamicadjustment of the spring force while the truck is in motion.

Spring only casters can range from hard, with a high spring constant, tosoft, with a low spring constant. A softer caster tolerates a rougherfloor, but also lets the truck tilt on turns and shifts in the load orthe operator position. A hard caster works well as long as the floor iscompletely flat. Conversely, the operator may sense rough floorconditions and objects on the floor, or cracks in the floor may effectthe truck as the caster rolls over them.

Other varieties of lift truck configurations use spring loaded castersand include a known shock absorber 34 for damping. The addition ofdamping allows for softer springs, but still reduces the oscillation ofrocking on a rough floor. Nevertheless, when one caster hits a largebump on the floor, the damper responds to the high speed motion of thecaster by generating considerable force and may tilt the truck becausethe damper force is a function of caster motion, not truck roll. Whenthe damper reacts in this way, it diminishes the advantages of softersprings.

Other varieties of lift truck configurations use a sway bar or torsionbar 36 between casters 24. Much like the spring and shock absorberconfiguration described above, with the inclusion of a torsion bar 36,the rough floor is averaged out so small random bumps don't tilt thetruck. When tilting to one side, it automatically reduces the springforce on the other, which may stop the tilt. But also like the springand shock absorber configuration, with a torsion bar, one caster hittingdebris may raise the caster on the other side. On the contact side, thecaster will push up while at the same time the caster on the other sideis being pulled up by the torsion bar. So, in some cases, the torsionbar may actually induce a tilt in the truck.

Referring to FIG. 3, still other varieties of lift truck configurationsuse fixed casters 38 and a suspended traction wheel 40. Thisconfiguration lets the suspension springs 42 provide enough force tokeep the traction wheel in contact with the floor, and is more prevalentwith very flat floors. On rough floors, operators of a truck with thisconfiguration are known to feel oscillations and the truck may tilt onmost every bump. Also, the effect of hitting an object with one castermay cause a significant contact and tilt.

The prior methods suffer from not monitoring the orientation of thetruck in one or more of the three axis of motion. For example, thecasters only need to put out a force when the truck is moving away fromhorizontal, or roll, in the X-axis 12. If the truck is horizontal, ornot changing quickly from horizontal, then the caster spring could bevery soft. Yet, all these existing solutions respond to vertical motionof the caster wheel regardless of whether it is tilting the truck ornot.

At best, the prior methods only improve the tradeoff between softsprings and the truck rolling versus hard springs and truck dampers thatlimit the performance of the spring only caster configurations. Anotherdisadvantage of these previously used methods has been that the force ormotion created is fixed. Even though variables like speed, mass anddirection of motion are changing constantly as the truck is used, thecompensating forces from a spring or shock are fixed, having beencalculated from average or nominal values. Therefore only a narrow rangeof motion can be effectively addressed or mitigated.

If the motion of the caster wheel can be mitigated or even cancelled,the truck would then be capable of traveling faster without thepotential damage to components or loss or degradation of truck data,along with a more comfortable ride for the operator. A more stablemounting platform for sensitive sensory components also improves thequality of data produced, allowing greater flexibility in the use of thetruck in either automatic or manual modes.

What is needed is a lift truck configured to retain desirable featuresof flexible casters and yet to add more stability control to the lifttruck.

SUMMARY OF THE INVENTION

The present invention overcomes the drawbacks of the previous lift trucksystems and methods by providing additional vibration control featuresto reduce or eliminate motion of the truck in one or more of the X-axis,Y-axis, and Z-axis. Some embodiments may include, alone or incombination with the vibration control, stability control to furtherstabilize the motion of the truck.

In one aspect, the present invention provides a lift truck havingvibration control. The lift truck comprises a tractor unit, withvertically movable forks mounted relative to the tractor unit, the forksbeing vertically movable between an upper position and a lower position.A vertical support is mounted relative to the tractor unit, and aplatform is mounted relative to the vertical support, the platform formounting electrical components. The vertical support comprises a hollowtube at least partially filled with a vibration damping material todamper vibrations from reaching the platform.

In one aspect, the present invention provides a method of reducingvibrations on a lift truck. The method comprises steps includingproviding a lift truck, the lift truck comprising a tractor unit andvertically movable forks mounted relative to the tractor unit, the forksbeing vertically movable between an upper position and a lower position.The steps also include providing a vertical support mounted relative tothe tractor unit; providing a platform mounted relative to the verticalsupport, the platform for mounting electrical components; dampingvibrations from reaching the platform with at least one of a vibrationdamping material in the vertical support and a mass-damper system; andproviding control circuitry coupled to the at least one of the vibrationdamping material and the mass-damper system to control a degree ofvibration damping.

The foregoing and other objects and advantages of the invention willappear in the detailed description which follows. In the description,reference is made to the accompanying drawings which illustratepreferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a lift truck showing three axis ofpossible motion;

FIG. 2 is a rear view of a lift truck, showing known spring loadedcaster configurations;

FIG. 3 is a rear view of a lift truck similar to the truck of FIG. 2,except showing a known fixed caster configuration with a suspendedtraction wheel;

FIG. 4 is a rear view of a lift truck similar to the truck of FIG. 1,and including embodiments of the invention;

FIG. 5 is a flow chart of an algorithm according to an embodiment of theinvention, the algorithm adapted to improve the stability of a lifttruck;

FIG. 6 is a schematic drawing of a system for improving the stability ofa lift truck in the Z-axis according to an embodiment of the invention;and

FIG. 7 is a schematic drawing of a system for improving the stability ofa lift truck by reducing the vibration in the lift truck.

The invention may be embodied in several forms without departing fromits spirit or essential characteristics. The scope of the invention isdefined in the appended claims, rather than in the specific descriptionpreceding them. All embodiments that fall within the meaning and rangeof equivalency of the claims are therefore intended to be embraced bythe claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The various aspects of the invention will be described in connectionwith improved stability and vibration control of industrial lift trucks.That is because the features and advantages that arise due toembodiments of the invention are well suited to this purpose. Still, itshould be appreciated that the various aspects of the invention can beapplied to achieve other objectives as well.

Embodiments of the invention described herein, either alone or incombination, are well suited to provide a dynamically stabilized lifttruck, including, for example, a dual-purpose fork lift truck that maybe operated as an automated robotic vehicle and also as a standardmanually operated truck. The truck achieves stabilization through one ormore individual or combined improvements that are configured to effectmotion in any one of three axes, and in some embodiments, plus reducevibration. The collective improvements provide protection for sensitiveelectronic components, increase operator comfort, and allow greaterproductivity by permitting faster travel speeds.

In addition, features of the invention allow for the creation of adynamically stable platform for mounting sensitive electroniccomponents, such as sensors, controls, and position detecting/reportingequipment, which allows the components to be more effective, regardlessof the floor conditions. The dynamically stabilized truck and platformallows the sensors and control equipment to generate better qualitydata, and to ensure more reliable operation. With better quality data,the truck may be allowed to travel faster due to more confidence in theaccuracy of the data it produces. And, when the truck can travel fasterand operate more reliably, the truck will likely generate moreproductivity.

The improved stability control systems and methods can be described asincluding a variety of unique features, where each feature canindividually contribute to the improved stability of the truck in is ownway, and each can be combined with one or more of the others tocontribute to the improved stability of the truck in combination.Therefore, each of the unique features will be described separatelybelow.

I. Active Roll and Pitch Control

Referring to FIG. 4, when a lift truck 50 strikes a floor condition thataffects only one side, such as when only one wheel, such as caster wheel52, strikes a crack 54 in the floor 56, and side 58 of the truck 50 isforced up due to the motion, the resultant side to side motion iscommonly called roll, and is shown as movement 70 about the X-axis 12.The effect of roll causes the entire truck to move or tilt to one side(the side 60 of the truck 50 with the wheel that did not strike thecrack), and mechanical and/or electronic components 64 such as anysensory equipment mounted on a platform 62 will also be directed to thesame side. The components 64, such as a sensor, mounted several feetaway from the original point of movement, such as the caster wheel 52,will have its reaction exaggerated. The sudden movement caused by thefloor condition can diminish the effectiveness of the electroniccomponents and may cause the truck to be operated at slower speeds toreduce the effects of the floor conditions. Slower operating speeds mayequate to an undesirable reduction in overall equipment productivity.Sudden movement at one or more wheels may result in an undesirableoverall vehicle movement and can be detected and mitigated by activelycontrolling one or more of the resultant forces in any of the threeaxis, for example one or both of pitch (rotation or movement about theY-axis) and roll of the truck.

As previously noted, prior methods suffer from not monitoring theorientation, e.g., pitch and/or roll of the truck. In an improved lifttruck, the casters only need to provide a reactant force when the truckis moving away from horizontal in either pitch or roll. If the truck ishorizontal, or not changing quickly from horizontal, then the casterspring could be very soft. Prior solutions respond to vertical motion ofthe caster wheel regardless of whether the vertical motion is tiltingthe truck or not.

Embodiments of the active roll and pitch control include a number offeatures:

1. Systems and methods measure the angular speed of rotation of thetruck 50 around the X-axis 12, the Y-axis 14, and in the Z-axis 16. Asdiscussed herein and as shown in FIG. 4, roll 70 is described as themovement, e.g., rotational speed, about the X-axis 12 in degrees persecond, or dps. Similarly, pitch 72 is described as movement, e.g., therotational speed, about the Y-axis 14. This angular speed of rotationaround the X and Y-axis may be measured to provide a numerical value ofthe measured roll 70 and/or pitch 72.

2. When the roll 70 and/or pitch 72 of the truck 50 exceeds apredetermined threshold value, the systems and methods may be configuredto “lock” one or more of the casters 52 to control the roll and/orpitch. In this context, “lock” means to stop the motion of the caster(s)in the Z-axis so it behaves like a fixed caster, or like a caster withan extremely hard spring. An actuator 76 locks the caster so it can actlike a fixed caster. A locked caster may not expand or retract, or itwould take great force to expand or retract, compared to an unlockedstate. In one embodiment, the motion of the caster is locked suddenly,and in an alternative embodiment, the motion is locked over apredetermined amount of time. The motion of the casters may also belocked in relation to other factors, such as speed of the truck, or theweight of the truck or load, or the height of the load, or steeringangle, or any combination.

3. After a predetermined duration of time, the casters may be unlocked.The predetermined duration of lock time for the locked casters may be afixed duration, or, similar to locking the motion of the castors, it maybe varied with vehicle speed and/or other factors. For example, at lowspeeds, the duration for locked casters may be longer than at highspeeds. In one embodiment, at very low speeds, with the load raised, allthe casters may be locked to create a temporary “fixed” caster truckconfiguration. Alternatively, the force on the left and right castersmay be sensed, and the sensed force on each caster may be compared todetermine when one or more of the casters could be unlocked.

Referring to FIG. 5, one embodiment of a method is shown for control ofcaster locking using feedback control of angular speed. It is to beappreciated that the systems and methods are adaptable for one or moreof the resultant forces in any of the three axis to control, forexample, either or both of pitch 72 and roll 70 together orindividually, and can use feedback of any of the factors describedabove, or other factors that would be known to one of skill in the art.

The caster locking/unlocking algorithm 80 may start with aninitialization process indicated as KEY ON at process block 82. At KEYON, the algorithm checks and/or adjusts, i.e., calibrates a GZEROstationary value 81 that represents zero degrees per second or “dps” fora GYRO signal 83 received from a gyroscope 84 while the truck isstationary. A gyroscope is preferably positioned at or generally near anaxis of rotation. Alternatively, one or more accelerometers 85 may beused and may be placed in other available locations on the truck. Inthis example, the GYRO signal 83 represents a roll 70, in dps, aroundthe X-axis 12. When the gyroscope 84 sends a signal having a dps valuegreater than the value of GZERO, the truck is rolling (i.e., tilting)over to the right at GYRO-GZERO dps. Likewise, a GYRO signal 83 having adps value smaller than GZERO indicates the truck is rolling (i.e.,tilting) to the left at GZERO-GYRO dps. In some embodiments, the KEY ONinitialization/calibration compensates for small shifts in the gyroscopesensor measurement.

In the embodiment shown, after the KEY ON initialization, the algorithmmay run in a loop 86, as shown. First, at LOOP CYCLE SPEED process block88, the algorithm waits a predetermined and possibly a fixed amount oftime to control how fast the loop 86 runs. In one embodiment, a 10milli-second wait time may be used, so, in this example, the loop cannotrun faster than 100 times a second. This example LOOP CYCLE SPEED waittime may be used to give mechanical actuators time to change states.Without allowing a sufficient amount of time for mechanical actuators tochange, the software may end up oscillating because it is able to changestate faster than the truck is able to change its motion. The LOOP CYCLESPEED wait time may generally be dependent on the truck design, the typeof actuators used to lock up the casters, and other delays inherent orbuilt into the system.

Next, at decision block 90, an absolute value of GYRO minus GZERO iscompared to a THRESHOLD dps value. In one embodiment, the system may beconfigured to stop tilts (e.g., pitch and/or roll) with a dps valueequal to or larger than the THRESHOLD dps value and not act upon smallerGYRO signals having a dps value less than or equal to the THRESHOLDvalue. During normal operation, there may be some minor pitches and/orrolls and the system may not react until the pitch or roll dps is at orexceeds THRESHOLD, typically where the GRYO signal is far from zero,although not a requirement. In a non-tilt example, if the GRYO signal isclose to zero, (and not more than THRESHOLD), then the algorithmcontinues to decision block 92, where it may simply check any locktimers (e.g., LOCK TIMER L, LOCK TIMER R) to determine if they are ON,and if they are, the algorithm continues to decision block 94 todetermine if any lock timers have been ON for a predetermined DURATION.If any timer is at or exceeds the DURATION, then the appropriate LOCKTIMER L or LOCK TIMER R may be turned OFF and reset, e.g., to zero msec.The loop 86 may then repeat by going back to process block 88, LOOPCYCLE SPEED. This permits a short predetermined period of time for thetruck to respond.

In a tilt scenario, the truck will start to tilt, and the GYRO signalwill shift away from GZERO by more than THRESHOLD. In this example, atdecision block 96, the algorithm determines which way the truck isrolling by whether the GYRO signal is larger than GZERO or smaller thanGZERO. Based on this determination, the algorithm branches to either theset LOCK R process block 98 or the set LOCK L process block 100, andlocks up the caster on that side for the pre-determined DURATION. TheLOCK R (or LOCK L) is set to ON, and the LOCK TIMER R (or LOCK TIMER L)is set to DURATION. The truck is thereby prevented from rolling in thatdirection and should, after some time delay, cause the GYRO signal toreturn to GZERO or at least make the absolute value of GYRO minus GZEROless than THRESHOLD.

Note that embodiments of the invention may allow the truck to tiltslowly. An advantage of the systems and methods described herein is thata rapid roll to either side or oscillation (rocking around the rollaxis) is stopped. For example, in one embodiment, a truck making asudden turn may have the outside caster lock up to prevent rolling asthe truck makes the turn. In another example, if a moving truck hits abump on the right caster, the left caster may lock up to preventrolling. But if the operator shifts the load and waits for severalDURATION periods, then the truck may slowly lean toward the heavy side.

This slow tilt feature of the invention is useful and important. Usefulbecause it lets the spring loaded casters adjust for wear so thetraction tire always has good contact force with the floor. The tractiontire may be the main source for control and braking, and it is importantthat the traction wheel maintain contact with the proper force againstthe floor surface.

After locking the appropriate side and starting the associated timer atprocess block 98 or process block 100, the algorithm repeats the loop 86by going back to process block 88, CYCLE SPEED LIMIT. During theDURATION period, the actuator 76 locks the left or right side caster 52so the caster acts like a fixed caster. In some embodiments, theactuator 76 could be a magneto-rheological (MR) fluid filled damper. Oneembodiment of an MR damper is able to lock up in about 20 milli-seconds,or more or less, while others are able to lock up in about 8 to 10milli-seconds, or more or less, and stop the caster from compressing thecaster spring 78. The caster may still have spring(s), but the springscould be soft so that a rough floor would not annoy the operator. TheDURATION period is set long enough to account for most shocks or tiltsdue to sharp turns or other obstacles that would tilt a truck with softor even hard springs. In one embodiment, a typical DURATION could rangefrom about 0.1 seconds to about 5 seconds, or more or less, and may bepredetermined in the algorithm for a particular truck design or truckapplication. In an alternative embodiment, the algorithm and associatedsystem may be able to adjust the DURATION period for long durations atlow speeds and shorter durations at high speeds. At high speeds, thetruck would complete the turn, or roll over the bump in the floor, in amuch shorter time than at low speeds.

Embodiments according to the invention provide several benefits andadvantages that cannot be obtained in existing truck configurations. Forexample, embodiments of the invention enable the truck to stay levelinstead of rocking due to uneven floors. This is beneficial to theoperator standing on the truck because a rocking truck may increaseoperator fatigue. In lifting loads onto or off of high racks or stacks,embodiments of the invention may lock both the left and right casters tomake the mast more stable and stay vertical. Embodiments of theinvention may also be more economical than fixed caster and floatingtraction wheel alternatives. Also, the ride quality may be much improvedover fixed casters that typically transmit every bump into the platformthe operator stands on. Embodiments of the invention will also allow useof very soft springs so the ride quality can be better than springcasters and spring-damper-caster designs. Notably, the invention detectsand stops the pitch and/or roll while other known alternative designs donot detect the truck pitch or roll.

A variety of alternative embodiments are contemplated for the invention,and may be included individually or in any combination.

In some alterative embodiments, a variety of actuators 76 arecontemplated for use with the invention. For example, small hydrauliccylinders with a rapid response profile are available. Also, solenoidbased actuators could use an electromagnet to lock the caster into afixed position. Pneumatic cylinders can be used to increase or decreasethe force of the caster on the floor in parallel with springs, or inplace of the mechanical springs. The MR actuator could act as a variabledamper that increases the mechanical resistance based on the rotationspeed (e.g., roll and/or pitch) instead of locking the caster solid.Hydraulic and pneumatic actuators can also act as sensors to detectcaster compression and measure, or predict, the truck tilting. Thehydraulic system could shut a valve to lock the caster, and thepneumatic system could open a valve to reduce pressure from acompressing caster or apply more pressure to extend a caster to exertmore force on the floor. Additional materials, including piezoelectriccomposites and electroactive polymers, or EAPs, are also contemplatedfor actuator use. Piezoelectric composites can be used for both sensorand actuator functions. Piezoelectric materials can convert electricalsignals into useful displacement or force. EAPs are polymers thatexhibits a change in size or shape when stimulated by an electric field.A beneficial characteristic property of an EAP is that they are able toundergo a large amount of deformation while sustaining large forces.

In other alternative embodiments, a variety of different sensors arecontemplated for use with embodiments of the invention. For example, avariety of gyroscope configurations are available, such as a solid stateMicro-electromechanical Systems (MEMS) gyroscope. There are also severalother types of gyroscope sensors or combinations of sensors that canreplace a true gyroscope. In other embodiments, the rotation of thetruck could be sensed by differential accelerometers, such as two Z-axisaccelerometers with one mounted on each side of the truck. For rollsaround the X-axis 12, the difference between the Z-axis 16 accelerationon the right and left side would indicate a roll is happening. Also, thetilt of the truck could be measured by mechanical devices used assensors. The compression of the spring 78 for each caster 52 could bemeasured by any type of proximity sensor. By using geometry, thevertical location of one or more of the casters can be used to infer thetruck tilt, or to predict that the truck will tilt due to unequalforces. In addition, hydraulic or pneumatic cylinders convert castercompression into a change in fluid pressure or fluid volume. Again, thevertical position of each caster, and the force it is exerting to tiltthe truck, can be inferred from measuring the fluid pressure or fluidvolume. For example, with a pneumatic cylinder, the contraction of thecaster will increase the gas pressure. For a hydraulic cylinder,compression of the caster will force fluid out of the cylinder and intoan expansion chamber. In addition to sensing or predicting truck tilt,these devices can also be used to lock the caster or apply force to stopthe truck tilting.

Other alternative embodiments are adaptable for a variety of differentapplications. In one application having the suitable arrangement oflockable casters, the pitch around the Y-axis 14 can be controlled justas the roll around the X-axis 12. In a scenario where the operator islifting a pallet high above the floor, the caster springs typicallyallow the truck mast to tilt, which is not desired. The tilting may makeit more difficult to put the load on a shelf. One possible applicationfor an embodiment of the invention would be to let the operatormanually, or the truck software automatically, lock one or more of thecasters while the load is some predetermined height above the floor. Inthis configuration, for example, for a short distance at low speeds, thetruck could have fixed casters that would keep the mast from tilting.

In yet additional alternative embodiments, the invention may embodypredictive control. For example, the truck may use power steering, ameasured steering angle, or have limit switches that indicate theposition of the steering controls. In these and other configurations,the truck software may anticipate the truck tilting due to steeringposition, truck speed, fork height above the floor, and/or other inputsfrom the operator. It is to be appreciated that the truck software couldtrigger a lock before the gyroscope 84 senses any tilt. And, thesoftware described may release the lock after DURATION has passed(assuming the gyroscope senses no rotation larger than THRESHOLD).

Other embodiments may utilize stability control parameters that may beaccessible on a local or remote computer system, such as a fleetmanagement system, for example, to set or adjust one or more stabilitycontrol parameters for a truck. Stability control parameters may be setor adjusted based on a variety of factors, such as type of truck, typeof load, load weight, and/or the operator, as non-limiting examples.Stability measurements that monitor truck motion, such as data fromaccelerometers and gyroscopes, may also be passed on to the fleetmanagement system. For example, the accelerometers can report impacts,and the gyroscopes may provide an indication that the truck casters needadjustment. This data may be recorded and available for analysis anddisplay on a system monitor, for example.

Other embodiments may use a wide range of systems and methods to adjustthe truck stability, and each may be used alone or in combination withother stability controls. Some embodiments may use a steered caster. Inthis configuration, the caster orientation may be monitored andcontrolled to maximize stability. In some other embodiments, a reductionin the permitted acceleration and speed of the truck could be used incombination with other systems and methods for stability control. Forexample, when a truck is turning, the casters may be locked to stop orreduce a roll. If that doesn't stop the roll, to a predetermined degree,then one or more factors affecting stability may be limited, such as theacceleration of the truck, and then another factor may be limited, suchas speed of the truck, and so on, to reduce or stop the truck roll.

II. Z-Axis Control

An additional aspect of the invention describes an embodiment of theinvention where movement in the vertical direction, the Z-axis 16, maybe controlled by dynamically suppressing movement of one or morevertical supports 110. Referring to FIGS. 4 and 6, a vertical support110 according to an embodiment of the invention may be composed of twoor more cylinders 112, 114 that function as a spring-mass-damper ortuned mass-damper system. Each vertical support may be constructedsimilar to a piston or hydraulic (pneumatic) cylinder and may be filledwith a spring 116 and a fluid 118 (e.g., air, liquid). The fluid 118 maybe ported to an orifice 120, such as a variable valve, and to areservoir 122. The orifice 120 may be electrically controlled via acontrol circuit 124, which may optionally include an amplifier 126, toallow a variable amount of fluid motion. In one embodiment, anaccelerometer 128 is used in the vertical axis (Z-axis 16) to detectmovement with respect to time. Single and multi-axis models ofaccelerometers are available to detect magnitude and direction of theacceleration. If the acceleration is high, for example, as from a suddenshock to the truck when contacting a bump, the control circuit 124 mayallow a fast fluid flow through the orifice providing cushioning, withthe spring 116, to a portion of the vertical support, effectivelyserving as a shock absorber. If the acceleration rates are small, thefluid movement may be limited, thereby keeping the vertical movementminimal. This embodiment is well suited to provide a more stableplatform 62 (see FIG. 4) for mounting components 64 on the verticalsupports 110. If the detected motion from a shock can be mitigated oreven cancelled, the truck may then be capable of traveling fasterwithout the potential adverse effects to components, or loss ordegradation of data. A more stable mounting platform for sensitivesensory components also improves the quality of data produced, allowinggreater flexibility in the use of the vehicle in either automatic ormanual modes.

III. Vibration Control

An additional aspect of the invention describes an embodiment of theinvention including vibration control. Vibration can develop in mostmechanical bodies during normal operation. While vibrations usually donot exhibit the same peak energy levels as the contact of an obstacle,it can cause other problems. Within a mechanical body, a vibration cancause small movements that occur at specific frequencies. In some cases,the mechanical structure, by virtue of its shape and mass, can developresonances that may have the effect of creating oscillations.

Vibration from truck movement over a floor surface can travel throughouta frame of the truck and anything attached to it. Referring now to FIGS.4 and 7, a vertical support 130 may be used for mounting the platform 62and associated components 64. The support 130 may transmit vibrationsexperienced from truck motion through the support 130 and to thecomponents 64. Damping the vibrations may be beneficial to the integrityof the sensor equipment and other components 64, and the quality of dataproduced. In one embodiment, construction of the vertical support 130may use hollow tubing 140. The tubing 140 may contain one or more plugsor sections 142 partially or completely filled with, for example, aphase changing, energy absorbing material such as Magneto-rheological(MR) fluid. The smaller particles within the MR fluid can move withrespect to each other and can dampen higher frequency vibration that thevertical support experiences. Piezoelectric materials and electroactivepolymers, for example, are also considered for use in tubing 140. Thephase changing material in the sections 142 may be electricallycontrolled via the control circuit 124, which may optionally include anamplifier 126, to allow a variable amount of phase change in the phasechanging material.

An alternative embodiment describes an active vibration dampening systembuilt into the support structure of the truck. In one embodiment, thesystem uses accelerometers 144 to detect vibration and movement both atthe mounting frame base 146 and at the stabilized platform 62. Vibrationfrequencies that are detected in the mounting frame 146 may travelthrough the tubing 140 to the platform 62 if not acted upon. Asdescribed above, in one embodiment, a phase changing or variableviscosity material may be used, such as MR fluid, to change the shape ofthe resonant cavity in the support structure tubing 140, therebydampening vibrations and/or any oscillations that start to occur.Because the truck may be moving with different speeds and with differentloads, the mass and dynamic conditions are likely to be constantlychanging. The active control is able to occasionally or continuouslychange the resonant characteristics of the support structure and preventvibrations from becoming parasitic oscillations that may cause unwantedresults.

In alternative embodiments, the tubing material 140 that the verticalsupport 130 is made from can be filled with one or more granular orpelletized materials 148, such as metal shot, plastic beads, or sand, asnon-limiting examples. The ability of the particles to move against eachother may help dissipate the higher frequency vibration energy andreduce and resultant undesirable motion. It is to be appreciated thatthe vertical support 130 can be mounted anywhere on the truck 50. It isalso to be appreciated that any of the above embodiments can be combinedto provide vibration control.

The foregoing has been a detailed description of illustrativeembodiments of the invention. Various modifications and additions can bemade without departing from the spirit and scope thereof. Furthermore,since numerous modifications and changes will readily occur to thoseskilled in the art, it is not desired to limit the invention to theexact construction and operation shown and described. For example, anyof the various features described herein can be combined with some orall of the other features described herein according to alternateembodiments. While the preferred embodiment has been described, thedetails may be changed without departing from the invention, which isdefined by the claims.

Finally, it is expressly contemplated that any of the processes or stepsdescribed herein may be combined, eliminated, or reordered. In otherembodiments, instructions may reside in computer readable medium whereinthose instructions are executed by a processor to perform one or more ofprocesses or steps described herein. As such, it is expresslycontemplated that any of the processes or steps described herein can beimplemented as hardware, software, including program instructionsexecuting on a computer, or a combination of hardware and software.Accordingly, this description is meant to be taken only by way ofexample, and not to otherwise limit the scope of this invention.

1. A lift truck having vibration control, the lift truck comprising: atractor unit; vertically movable forks mounted relative to the tractorunit, the forks being vertically movable between an upper position and alower position; a vertical support mounted relative to the tractor unit,and a platform mounted relative to the vertical support, the platformfor mounting electrical components; and the vertical support comprisinga hollow tube at least partially filled with a vibration dampingmaterial to damper vibrations from reaching the platform.
 2. The lifttruck as set forth in claim 1 further including a first sensor toprovide a first value of motion of the lift truck in at least one of anX-axis and a Y-axis and a Z-axis.
 3. The lift truck as set forth inclaim 2 wherein the first sensor comprises a first accelerometer.
 4. Thelift truck as set forth in claim 3 wherein the first accelerometer ismounted relative to the platform.
 5. The lift truck as set forth inclaim 2 further including a second sensor to provide a second value ofmotion of the lift truck in at least one of the X-axis and the Y-axisand the Z-axis.
 6. The lift truck as set forth in claim 5 wherein thesecond sensor comprises a second accelerometer.
 7. The lift truck as setforth in claim 6 wherein the second accelerometer is mounted relative tothe tractor unit.
 8. The lift truck as set forth in claim 1 wherein thehollow tube includes at least one hollow portion separated by a dampersection, the damper section containing the vibration damping material.9. The lift truck as set forth in claim 8 wherein the vibration dampingmaterial comprises at least one of a magneto-rheological fluid, apiezoelectric material, an electroactive polymer, and a granularmaterial.
 10. The lift truck as set forth in claim 8 wherein the atleast one hollow section contains a granular material.
 11. The lifttruck as set forth in claim 1 further including a mounting frame base,the vertical support mounted relative to the mounting frame base. 12.The lift truck as set forth in claim 5 further including controlcircuitry coupled to at least one of the first and second sensors andthe vibration damping material to control a degree of vibration damping.13. The lift truck as set forth in claim 12 wherein the vibrationdamping material is a phase changing material.
 14. The lift truck as setforth in claim 12 further including at least one caster mounted relativeto the tractor unit; and an actuator to lock movement of the caster on aside of the lift truck based on a direction that the control circuitrydetermined the lift truck to be moving.
 15. A lift truck havingvibration control, the lift truck comprising: a tractor unit; verticallymovable forks mounted relative to the tractor unit, the forks beingvertically movable between an upper position and a lower position; avertical support mounted relative to the tractor unit, and a platformmounted relative to the vertical support, the platform for mountingelectrical components; the vertical support comprising two or morecylinders that function as a mass-damper system to damper vibrationsfrom reaching the platform, the mass-damper system include a spring, afluid, and a variable valve; and control circuitry coupled to thevariable valve, the control circuitry to control a flow of the fluidthrough the variable valve to control a degree of vibration damping. 16.The lift truck as set forth in claim 15 further including a sensorcoupled to the control circuitry, the sensor to provide a value ofmotion of the lift truck in at least one of an X-axis and a Y-axis and aZ-axis.
 17. The lift truck as set forth in claim 16 wherein the sensorcomprises an accelerometer.
 18. The lift truck as set forth in claim 17wherein the accelerometer is mounted relative to the platform.
 19. Thelift truck as set forth in claim 16 wherein the value of motion providedby the sensor is used to control the flow of fluid through the variablevalve.
 20. The lift truck as set forth in claim 15 further including atleast one caster mounted relative to the tractor unit; and an actuatorto lock movement of the caster on a side of the lift truck based on adirection that the sensor determined the lift truck to be moving. 21.The lift truck as set forth in claim 15 wherein the platform includespositioning equipment.
 22. A method of reducing vibrations on a lifttruck, the method comprising: providing a lift truck, the lift truckcomprising: a tractor unit; and vertically movable forks mountedrelative to the tractor unit, the forks being vertically movable betweenan upper position and a lower position; providing a vertical supportmounted relative to the tractor unit; providing a platform mountedrelative to the vertical support, the platform for mounting electricalcomponents; damping vibrations from reaching the platform with at leastone of a vibration damping material in the vertical support and amass-damper system; and providing control circuitry coupled to the atleast one of the vibration damping material and the mass-damper systemto control a degree of vibration damping.
 23. The method as set forth inclaim 22 further including providing a sensor coupled to the controlcircuitry, the sensor to provide a value of motion of the lift truck inat least one of an X-axis and a Y-axis and a Z-axis.
 24. The method asset forth in claim 23 further including providing at least one castermounted relative to the tractor unit; and activating an actuator to lockmovement of the caster on a side of the lift truck based on a directionthat the sensor determined the lift truck to be moving.